1. Field of the Invention
The present invention is directed generally to an electromechanical relay and, more particularly, to an RF relay with high insertion loss repeatability.
2. Description of the Background
Ultraminiature electromechanical relays are used in many test equipment circuits, instrumentation circuits, communication circuits, attenuator circuits, RF signal pulse generator circuits, tower mount amplifier bypass circuits, and other applications where signals are at low power levels and high frequencies. In such applications, it is expected that a relay's radio frequency (RF) insertion loss value is repeatable over the applied signal frequency range. Thus, when the system which contains the relay is calibrated to an RF insertion loss value at some frequency, it is expected that the RF insertion loss value of the signal path through the relay shall be the same value or repeat within an acceptable maximum deviation on subsequent operation of the device in which the relay is incorporated. General purpose direct current (DC) ultraminiature electromechanical relays were not specifically designed to handle RF signals and thus do not provide repeatable RF output signals through the relay signal path for the applicable frequency band with high reliability.
The relevant art has incorporated coil shims in relays with tall frames and long coils to provide structural support for the motor assembly components. Relevant art relays with short frames and short coils do not include coil shims. However, the coils shims were not added with the express purpose of improving the RF performance of the relays. The relevant art has also incorporated a cutout section in the coil shim of relays with tall coils near the forward actuator bead end of the armature when the relays are in the de-energized state. Such cutout sections are not bent and are used as identification marks.
FIG. 14 is a diagram illustrating a relay 10 from the relevant art. The relay 10 is shown in its de-energized state, i.e. when no voltage is applied across coil 12. The relay 10 includes a stop component 14 which is welded to the top side of a header seal assembly base 16. The stop component 14 limits the clockwise rotation, or downward movement, of an armature assembly 18 in the relay 10. When the coil 12 is de-energized, the armature 18 rests on the stop component 14. The stop component 14 may be adjusted up or down to vary the gap between the armature 18 and a motor assembly frame pole face 20. The moment arm from a fulcrum edge 21 of a core assembly 19 to where the stop component 14 is located is larger than the moment arm from the fulcrum edge 21 of the core assembly 19 to the point where a return spring 17 pushes against the armature 18. Thus, the normal force at the stop component 14 to the corresponding armature 18 location is relatively small.
The relay 10 has the disadvantage that it does not have significant reliability of RF signal repeatability over the frequency range of low frequencies to frequencies of 3 GHz and above because the relay does not provide an effective ground circuit for RF signals when it is in the de-energized state. RF signals which travel along the path of moving contacts 15 and upper stationary contacts 13 radiate, or leak out of the path. The radiation causes signal losses at random, resulting in non-repeatability of the relay's RF insertion loss characteristics during operation. Thus, there is a need for a relay that has an RF insertion loss value which is repeatable over the applied signal frequency range.